Method for removing arsenic from metals or alloys

ABSTRACT

Arsenic contained in ferronickel, pig iron, steel or crude nickel is effectively removed by adding at least one of calcium material, magnesium material and carbon material to the molten metal. Examples of the calcium material are Ca-Si, CaC2, etc.; those of the magnesium material are Si-Mg, MgF2, etc. and those of the carbon material are cokes powder, charcoal powder, etc.

United States Patent Inventors Noboru Hayashl Amagasakl-shi; HidemiKaida, Kakogawa-shi; Teruo Takatsuki, Nlshlnomlya-shl, all 01 JapanAppl. No. 799,927 Filed Feb. 17, 1969 Patented Nov. 23, 1971 AssigneeKobe Steel, Ltd.,

Kobe-shi, Japan Priority Feb. 15, 1968 Japan 43/9751 METHOD FOR REMOVINGARSENIC FROM METALS OR ALLOYS Primary Examiner-L. Dewayne RutledgeAssistant Examiner-G. K. White Attorney-Jecies and Greendise ABSTRACT:Arsenic contained in ferronickel, pig iron. steel or crude nickel iseffectively removed by adding at least one of calcium material,magnesium material and carbon material to the molten metal. Examples ofthe calcium material are Ca-Si, CaC etc.; those of the magnesiummaterial are Si-Mg, MgF etc. and those of the carbon material are cokespowder, charcoal powder, etc.

METHOD FOR REMOVING ARSENIC FROM METALS OR ALLOYS This invention relatesto a method for effectively removing arsenic contained in metals oralloys, and more particularly, it concerns a method for removing arseniccontained in metals or alloys which comprises adding to molten metalcontaining arsenic at least one of calcium materials, magnesiummaterials and carbon materials as reducing agent.

It is well known that arsenic which cannot be removed in the usual stepsfor producing pig iron and steel remains in the final product as animpurity and most steels contain arsenic as one of the elements whichare contained in a small amount. Many researches have been made onefi'ects of arsenic on steel and ferroalloys to find that it has badeffects thereon. For example, regarding steel, arsenic lowers themechanical properties and further causes red shortness to damage the hotworkability. Regarding cast iron, arsenic lowers physical propertiessuch as growth resistance and heat resistance, and mechanical propertiessuch as impact value, tensile strength and deflection resistance, andfurther prevents spheroidizing of graphite. Arsenic has no good effectson any characteristics of steel or cast iron.

The conventional methods for removing arsenic from steel or ferroalloyswhich have been carried out by vaporization in vacuum or application oflow frequency vibration require a special melting apparatus and furtherthey are not satisfactory on the loss of iron, the efficiency forremoval of arsenic and the reproducibility. Therefore, a method foreffectively removing arsenic under normal pressure using theconventional smelting furnace or ladle has been waited for.

An object of this invention is to provide a method for simply andeffectively removing arsenic from steel or ferroalloys which requires noexpensive and special apparatus. Said ob ject can be attained by addingto molten metal or alloy at least one of calcium materials, magnesiummaterials and carbon materials as reducing agent.

Arsenic belongs to Group V of the Periodic Table to which phosphorousalso belongs and is a metal having the physical properties similar tothose of phosphorus. However, it is impossible to remove arsenic as anarsenic oxide by the addition of lime, iron oxide and the like as in thedephosphorization of molten iron. That is, arsenic can be easily removedas an oxide in roasting of an ore, but when once the ore is reduced toproduce metal iron and when arsenic is contained in the molten iron,arsenic cannot be removed as an oxide and rather it has beenacknowledged that the concentration of arsenic is increased with theincrease of the degree of oxidation atmosphere. Therefore, it isconsidered that although arsenic has the physical characteristicssimilar to those of phosphorus,

the former is removed in a mechanism different from that of 50 theremoval of the latter.

The inventors made various experiments to establish the above facts.Further, as the results of various experiments strongly reducingatmosphere. That is, arsenic contained in molten metal can be removed byadding to said molten metal a proper amount of at least one materialselected from the group consisting of calcium materials, magnesiummaterials and carbon materials. Furthermore, the efl'ects of the methodof the invention are further heightened by stirring the resultantmixture. Said stirring may be carried out by the known method such as bytop pouring method or by human power with a graphite rod or by a shakingladle. The added reducing agent covers the surface of the molten metalas a slag and keeps equilibrium between the molten metal and atmosphereunder reducing state.

The method of this invention is effective for removal of arsenic inferronickel, but may be advantageously applicable to other ferroalloys,steel, pig iron, crude nickel, etc.

The examples of said reducing agent to be added to the molten metal areas follows:

Calcium materials ..Ca, CaSi, Ca Si, CaSiz, Ca-Si, Ca-Si-Al. Ca-Si-Mg,Ca-Fe-Si, RI- Ca-Si] (R is a rare earth element such as Ce), CaC CaH CaFCaISiFQ].

Mg, Si-Mg, Ni-Mg, Cu-Mg, Mg-Coke. MgFz. MgClg.

MgISiFs].

Carbon materials ..coke powders, charcoal powders, anthracite powders.

electrode powders.

Further, the addition amount of said reducing agent which is expressedby the amount of element Ca, Mg or C is as follows:

Calcium materials" .Ca: 3.0l2% by weight, preferably about 6.2%.Magnesium materia .Mg: 2.08.0% by weight, preferably about 3.5%. Qarbonmaterials ..C: 4.0-l6.0% by weight, preferably about 12.0%.

When two or more of the reducing agents are added, the

amounts thereof should meet the following equation.

Mg+( 2/4) C+( 2/3) Ca=28 The upper limit of the amount of each reducingagent was experimentally determined in view of economical point andeffect of removal of arsenic and the lower limit was also experimentallydetermined in view of the effect of removal. When the amount of thereducing agent is below the lower limit, almost all of the agent isconsumed for desulfurization and removal of arsenic cannot be attained.

The calcium materials are especially suitable for removal of arseniccontained in ferronickel and the magnesium materials are suitable fortreatment of pig iron.

The following examples are intended to illustrate the invention.

Magnesium materials Examples To about kg. of each molten metal offerronickel, pig iron, steel, and crude nickel which were molten in ahigh frequency furnace and contained arsenic, suitable amounts of saidvarious reducing agents were added to keep the molten metals at astrongly reducing atmosphere and the mixture was vigorously stirred byhuman power or by using a shaking ladle. The results obtained are shownbelow.

1. Fe-Ni (25% Ni) was treated with calcium materials as reducing agents.

TABLE 1 Amount of Time As (percent) Removing addition of percentageReducing (percent by Manner of stirring Before After for arsenic TestNo. agent weight) stirring (min.) treatment treatment (percent) 1Additive B 3. 4 Human power 5 0.23 0. 14 3!). l C C 4 d 6 0,34 0.12 64.76 d0 12 0.27 0.05 81.5 8 Shaking ladle 7 0. 34 0.03 91. 2 8 Human power12 0.28 0.03 89. 3 12 0.28 0.01 96. 5 12 0.30 0. 02 93. 3

using reducing atmosphere, not oxidizing atmosphere, they found thatremoval reaction of arsenic progresses under 2. Fe-Ni (25% Ni) wastreated with magnesium mater TABLE 2 Amount of Time As (percent)Removing addition 0 percentage Reducing (percent by Manner of stirringBefore After for arsenic Test No agent weight) stirring (min.) treatmenttreatment (percent) 4 Human power. 1G 0. 34 0.20 41. 2 12 0.30 0. 14 53.3

6 Shaking ladle.

3. Pig iron was treated with calcium materials.

TABLE 3 Amount of As, percent Removing addition, Time of percentagepercent by Manner of stirring, Before After for arsenic Test No.Reducing agent weight stirring min. treatment treatment percent l CaCz,additive B. l Shaking 8 0.23 0.10 56.

5. 1 ladle. 2 C802, additive A.. 8 0.25 0. 09 64. 0

3 C8Cz, additive A.. 8 0.28 0. 09 07. 0

8 0.21 0.08 61. 0 l0 0. 20 0. 06 82. 7 0.28 0.03 Nil. 2

4. Pig iron was treated with magnesium materials.

TABLE 4 Amount of As, percent Removing addition, Time of percentagepercent by Manner of stirring, Before After for arsenic, Test No.Reducing agent weight stirring min. treatment treatment percent 1Mg-coke 4 Shlaling 8 0. 22 0.06 72. 7

a e. 2 d0 6 do 8 0.22 0.04 81. 8

5 Pig iron was treated with carbon materials.

TABLE 6 Amount of As, percent Removing addition, Time of percentagepercent by Manner of stirring, Before After for arsenic. Test No.Reducing agent weight stirring min. treatment treatment percentElectrode powder. 6 siliaging 0.30 0. 25 16.7

a e. 2 Cokes powder "do..." 15 0.29 0.16 48.3

6. Steel was treated with calcium materials.

TABLE 6 Amount oi As, percent Removing addition, Time of percentagepercent by Manner of stirring, Before Aiter for arsenic, Test No.Reducing agent weight stirring min. treatment treatment percent 1 CaCz,additive A. 2 Human 0.12 0.06 50.0

power. 2 CaCz 6 do 8 0.12 0.03 69.2

7. Crude nickel was treated with calcium materials and magnesiummaterials.

TABLE 7 Amount of As, percent Removing addition, Time of percentagepercent by Manner of stirring, Before After for arsenic, Test N 0.Reducing agent weight stirring min. treatment treatment percent 1 C801'1 Human 10 1. 34 0.85 6- Mg-coke 4 Power.

Note:

I. Additive A comprises 70 parts of CaSi and 10 parts of MgF,. AdditiveB comprises 60 parts of Ca-Si and five parts of MgF,.

2. Composition of Ca-Si...Ca 33% Si 67% Composition of Mg-Coke...Mg Coke3. Chemical composition of Fe-Ni (25% Ni) is as follows:

stances, said method comprisin forming a melt of said substance andadding to the melt, or removing arsenic, at least one reducing agentselected from the group consisting of calcium, magnesium and carbonmaterials, the amount of arsenic 70 removed being from about l6.7 to96.5 percent.

2. A method according to claim I, wherein said calcium material is amember selected from the group consisting of Ca,

Ni C0 A5 C Bi 8 Cu Cr 24.74 0.43 0.28 0.02 0.01 0.021 0.03 0.03

CaSi, Ca Si, CaSi Ca-Si, Si, Ca-Si-al. CaSiMg. Ca-Fe-Si, R[-CaAYSi], CaCCal-i CaF, and Ca[SiF 3. A method according to claim 1, wherein saidmagnesium material is a member selected from the group consisting of mg.Si-Mg Ni-Mg Cu-Mg Mg-coke, MgF MgCl and Mg[SiF.,.

4. A method according to claim I. wherein said carbon material is amember selected from the group consisting of cakes powders, charcoalpowders, anthracite powders and electrode powders.

5. A method according to claim 1, wherein said calcium material is addedin an amount by weight of 3.0-l2 percent expressed by the amount ofelement calcium.

6. A method according to claim 1, wherein said magnesium material isadded in an amount by weight of 2.0-8.0 percent expressed by the amountof element magnesium.

7. A method according to claim 1, wherein said carbon material is addedin an amount by weight of 4.0-l 6.0 percent expressed by the amount ofelement carbon.

11. A method according to claim 1. wherein Ca-Si and MgF; are added.

12. A method according to claim I, wherein Ca-Si, MgF and CaC are added.

13. A method according to claim I, wherein CaC and Mg-coke are added.

2. A method according to claim 1, wherein said calcium material is amember selected from the group consisting of Ca, CaSi, Ca2Si, CaSi2,Ca-Si, Ca-Si-Al, Ca-Si-Mg, Ca-Fe-Si, R(-Ca-Si), CaC2, CaH2, CaF2 andCa(SiFb).
 3. A method according to claim 1, wherein said magnesiummaterial is a member selected From the group consisting of Mg, Si-Mg,Ni-Mg, Cu-Mg, Mg-coke, MgF2, MgCl2 and Mg(SiF6).
 4. A method accordingto claim 1, wherein said carbon material is a member selected from thegroup consisting of cokes powders, charcoal powders, anthracite powdersand electrode powders.
 5. A method according to claim 1, wherein saidcalcium material is added in an amount by weight of 3.0-12 percentexpressed by the amount of element calcium.
 6. A method according toclaim 1, wherein said magnesium material is added in an amount by weightof 2.0-8.0 percent expressed by the amount of element magnesium.
 7. Amethod according to claim 1, wherein said carbon material is added in anamount by weight of 4.0-16.0 percent expressed by the amount of elementcarbon.
 8. A method according to claim 1, wherein at least two materialsare added in an amount by weight which satisfy the following equation,Mg+2/4C+2/3Ca 2-8%.
 9. A method according to claim 1, wherein the metalto be treated is a member selected from the group consisting offerronickel, steel, pig iron and crude nickel.
 10. A method according toclaim 1, wherein the molten metal to which the material is added isvigorously stirred.
 11. A method according to claim 1, wherein Ca-Si andMgF2 are added.
 12. A method according to claim 1, wherein Ca-Si, MgF2and CaC2 are added.
 13. A method according to claim 1, wherein CaC2 andMg-coke are added.